A161904 Array read by rows in which row n list the divisors of n, but if n is a square then the square root of n appears repeated. Also, the divisors appear as pairs (a,b), where a <= b, such that a*b = n.

1, 1, 1, 2, 1, 3, 1, 4, 2, 2, 1, 5, 1, 6, 2, 3, 1, 7, 1, 8, 2, 4, 1, 9, 3, 3, 1, 10, 2, 5, 1, 11, 1, 12, 2, 6, 3, 4, 1, 13, 1, 14, 2, 7, 1, 15, 3, 5, 1, 16, 2, 8, 4, 4, 1, 17, 1, 18, 2, 9, 3, 6, 1, 19, 1, 20, 2, 10, 4, 5, 1, 21, 3, 7

Offset

1,4

Comments

Row lengths are 2*A038548(n). - R. J. Mathar Jun 28 2009

Links

Table of n, a(n) for n=1..74.

Example

Array begins:
(1,1);
(1,2);
(1,3);
(1,4),(2,2);
(1,5);
(1,6),(2,3);
(1,7);
(1,8),(2,4);
(1,9),(3,3);
(1,10),(2,5);
(1,11);
(1,12),(2,6),(3,4);
(1,13);
(1,14),(2,7);
(1,15),(3,5);
(1,16),(2,8),(4,4);

Crossrefs

See also A161901 for another version.

Cf. A000005, A027750, A038548, A161841.

Sequence in context: A238800 A067734 A303758 * A360678 A346697 A338565

Adjacent sequences: A161901 A161902 A161903 * A161905 A161906 A161907

Keyword

easy,nonn,tabf

Author

Omar E. Pol, Jun 23 2009

Extensions

Keyword tabf added by R. J. Mathar, Jun 28 2009

Status

approved